1. Field of the Invention
The present invention relates to a system for storing related and unrelated data items on a plurality of removable recordable media instances (RMIs), and more particularly to a system which will reserve RMI storage space so that related data items are grouped together even though they are stored at different times.
2. Discussion of the Related Art
The grouping of information by subject matter is basic to any library. For instance, in a library for books, the librarian typically reserves shelf space for a subject book, particularly when the subject matter is an active one. While this is relatively easy for a book library, it is much more difficult to arrange subject matter on electronic media in electronic storage devices. With electronic media, one deals with data items instead of books. A data item can be a word, a sentence, a normal book, larger than a normal book, or any size of drawing. When a number of electronic media producers or processors, such as personal computer workstations, store data items, it is more efficient to store these data items at a central location rather than on individual memories of the personal computers. For example, if a large number of people were working at various personal computer workstations to develop and process data items which are required for a large project, such as building a missile, it would be desirable that each one of these data items be classified by subject matter and stored at a remote location for retrieval by any one of the workstation users. In order to make the retrieval of this information efficient, it is necessary that related subject matter be grouped into a common location within the remote storage device so that the accessing device does not have to access related data items from one end of the storage device to the other.
A prior art data file storage management system, available from the assignee of this application, eliminates the need for individual workstation users or groups of users to perform data storage space management on their limited storage devices. The system is a distributed file storage management system and is sold under the trademark "DFSMS", which is owned by the IBM corporation. With this system, space management is handled by a storage administrator who can cause data storage space requests from distributed workstation sites to be allocated based upon particular parameters dictated by the enterprise being served. The DFSMS system is primarily focused on permanently mounted storage media of the direct access storage device (DASD) type. This focus did not address the methodologies for effective utilization and optimization of storage and retrieval of data residing on media which is not permanently mounted.
The object access method (OAM), a component of a data facility product (DFP)/multiple virtual storage (MVS) available from the IBM Corporation stores data on "write-once-read-many" (WORM) optical media in a form that is permanent, as opposed to storage of erasable data on magnetic media. The advantage of optical media is that it can contain very large quantities of data and it can be demounted to allow other media to be used on the same optical read/write device. These optical read/write devices are placed in an optical library that can store many optical media volumes and mount/demount these volumes in one or more available optical read/write devices.
Currently, OAM stores data on any eligible optical media that is already mounted using the storage group constraints of the DFSMS product. The problem is that this can result in data being scattered across multiple instances of optical media in an optical library. This creates a retrieval problem in that two or possibly many more optical media must be mounted before all of the data needed by an application is made available.
The need is for a system for storing logically related data on the same or as few as possible removable recordable media instances (RMIs), such as optical disks or magnetic tape cartridges, so that this related data can be quickly accessed when the user desires to retrieve information on any particular subject. This system has to work regardless of time constraints. For instance, a piece of data may be stored today, then many months may pass before another piece of data, related to the first stored data, is stored. Accordingly, the system has to reserve storage space on the RMI on behalf of a system external to the RMI so that when the related data item arrives many months later it will be stored in proximity to the first stored data item. With such an arrangement, removable recordable media, such as optical disks and magnetic tape cartridges, can be efficiently utilized to store a large group of related data items which may be submitted for storage in multiple, separate transactions.